The production of oxirane compounds such as propylene oxide and its higher homologs is described in Kollar U.S. Pat. No. 3,351,635. In accordance with the Kollar process, the oxirane compound may be prepared by epoxidation of an olefinically unsaturated compound (for example, propylene) by use of organic hydroperoxide and a suitable metal catalyst, such as a molybdenum compound. Kollar teaches that activity of the metal catalyst disclosed therein for expoxidation of primary olefins is high and can lead to high selectivity of propylene to propylene oxide. These selectivities are obtained at high conversions of hydroperoxide (50% or higher) which conversion levels are important for commercial utilization of this technology. In accordance with the Kollar process, the epoxidation reaction proceeds under pressure in a liquid state, and accordingly, a liquid solution of the metal catalyst is desired.
In the preparation of metal compounds, for example, molybdenum salts, for the aforementioned purposes, various techniques have been used, many of which have been found to be extremely difficult to carry out efficiently on a commercial scale, and hence expensive, particularly for preparing hydrocarbon soluble compositions containing a high molybdenum content. Kollar U.S. Pat. No. 3,362,972 is concerned with preparation of molybdenum salts of carboxylic acids wherein molybdenum trioxide is reacted with oxalic acid in the presence of hexanoic acid. Sheng et al. U.S. Pat. No. 3,434,975 reports the preparation of molybdenum containing catalysts by reaction of molybdenum metal with peroxy compounds in the presence of a saturated alcohol. Sheng et al. U.S. Pat. No. 3,453,218 discloses the preparation of molybdenum containing epoxidation catalysts by reaction of molybdenum metal with a combination of tertiary butyl hydrogen peroxide and formic acid at low temperature. Ziolkowski et al. Polish Pat. No. 100,561 discloses the preparation of molybdenum-containing catalysts by treating Mo(OH).sub.5 with certain aliphatic or dicarboxylic acids and with an alpha-hydroxy acid or with certain diols or beta-diketones in an organic solvent. Ziolkowlski et al. Polish Pat. No. 103,742 is concerned with preparation of complexes of molybdenum from Mo(O)(OH).sub.3 and oxalic acid, lactic acid and ethylene glycol deposited on certain carriers. Sobczak et al., Journal Less-Common Met., Vol. 54, pp. 149-52 (1977) describe the reaction of molybdenum complexes with dicarboxylic acids, such as oxalic acid. Finally, Kuzimina et al., Izv. Timiryazev. Sel'skokhoz Akad. (2), 224-8 (1970) describe complex forming reactions of molybdenyl ions with certain organic dicarboxylic acids, including oxalic acid.
However, each of these prior art processes are deficient by requiring expensive starting materials or forming carboxylates or complex molybdenum compositions which contain relatively low metal content and/or in requiring a number of steps in order to produce the desired high molybdenum-containing soluble catalyst composition.
Accordingly, it is an object of the present invention to provide a simple, inexpensive method for the production of molybdenum-containing catalysts having a high metal content which are suitable for use in the epoxidation of olefins with organic hydroperoxides to produce the corresponding oxirane compounds.
A further object of the present invention is to provide molybdenum-containing catalyst compositions which result in increased selectivity to desired alkylene oxide, e.g. propylene oxide, product in the epoxidation of a primary olefin, e.g. propylene while at the same time reducing production of undesired by-products.
An additional object of the present invention is to provide a process for the preparation of molybdenum-containing epoxidation catalysts from molybdenum metal, which process is characterized by improved dissolution rates of the molybdenum metal, thereby reducing hydroperoxide consumption, lowering molybdenum losses and providing catalyst preparation at increased productivity.